Wheel and gear assembly

ABSTRACT

A wheel assembly is disclosed, in which a ring gear is movably mounted to the rim of the wheel, so that torque can be transmitted between wheel and rim, while the ring gear is isolated from deformations induced in the wheel rim.

RELATED APPLICATIONS

The present application is a National Phase of International ApplicationNo. PCT/GB2015/050740, filed Mar. 13, 2015, which claims priority fromGreat Britain Application No. 1404636.1, filed Mar. 14, 2104.

FIELD OF THE INVENTION

The present invention relates to a mounting arrangement for mounting aring gear or sprocket to a hub of an aircraft wheel.

BACKGROUND OF THE INVENTION

Aircraft are required to ground taxi between locations on airfields. Anexample is taxiing between a runway and the location (e.g. terminalgate) at which the aircraft's passengers are to hoard or disembark.Typically, such taxiing is achieved by using the thrust from theaircraft's engines to propel the aircraft forwards so that the landinggear wheels are caused to rotate. Since ground taxi speeds arenecessarily relatively low, the engines must be run at a very low power.This means that there is a relatively high fuel consumption as a resultof the poor propulsion efficiency at this low power. This leads to anincreased level of both atmospheric and noise pollution locally aroundairports. Moreover, even when the engines are run at low power it isgenerally necessary to apply the wheel brakes to limit ground taxispeeds, leading to a high degree of brake wear.

Reversing of a civil aircraft, e.g. away from a terminal gate, using itsmain engines is not permitted. When reversing is necessary, or in othersituations where ground taxiing via main engine thrust is notpracticable, tow trucks are used to manoeuvre aircraft around. Thisprocess is laborious and costly.

There is therefore a need for a drive system to power the wheels of anaircraft landing gear during ground taxi operations. There is also adesire to use such a drive system to pre-spin the wheels prior tolanding, so that the wheels are already spinning at, or near, theirinitial landing speed on touch down. Such pre-landing spin-up isperceived to reduce tyre wear on landing, and reduce loads transmittedto the landing gear during landing.

Several autonomous ground taxi systems for both driving the wheels whilethe aircraft is on the ground and spinning them up prior to landing havebeen proposed in recent years.

An example is disclosed in US2006/0065779, which proposes a powered noseaircraft wheel system in which a clutch is used to switch between a modein which the wheel can spin freely and a mode in which the wheel can bedriven by an electric motor. The clutch can also operate to enable themotor to pre-spin the wheel prior to landing.

Such prior art systems are typically limited to nose landing gearsbecause they take up too much space to be able to be integrated into amain landing gear in which much of the space around the wheels is takenup by braking systems. However, nose landing gears only support a smallfraction of the vertical loads supported by the landing gear as a wholeduring ground taxi operations (approximately 5% of the aircraft weight).There may therefore be insufficient traction between a driven noselanding gear wheel and the ground to enable reliable aircraft groundtaxiing. This is a particular concern when the aircraft centre ofgravity is towards its aft limit and when the ground surface isslippery.

A prior art arrangement which is not restricted to nose landing gears isdescribed in WO2011/023505. The disclosed system uses an actuator tomove a pinion gear in and out of driving engagement with a ring gearmounted to the wheel hub.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a wheel assembly, comprising:

-   -   a wheel;    -   a ring gear, mounted to and rotatable with the wheel; and    -   an interface for connecting the wheel hub to the ring gear to        transmit a torque therebetween;    -   the interface comprising:        -   an array of substantially radially oriented openings,            arranged in a substantially circular array around an axis of            rotation of the assembly; and        -   a plurality of connecting members disposed in the openings,            each connector having a substantially radially oriented            longitudinal axis, the connecting members being free to move            relative to at least one of the wheel hub and the ring gear,            to permit relative radial movement between the ring gear and            the wheel hub;    -   such that torque applied to one of the ring gear or the wheel is        transmitted to the other via the connecting members, and the        ring gear is substantially isolated from radial deformation of        the wheel rim.

The wheel assembly of the invention provides for radial isolation of thering gear from deformations of the wheel rim while permitting torque tobe transmitted through the interface.

The interface may provide a radial clearance on a connection pathbetween the wheel hub and the ring gear.

The interface may comprise a lateral extension to the wheel rim or ringgear, extending in a direction of the axis of rotation of the wheel orring gear on which it is provided.

The lateral extension may comprise a grow-out provided on at least oneof the wheel and the ring gear.

The lateral extension may comprise a series of laterally extending tabsprovided on one of the wheel or the ring gear.

The interface may be provided between the lateral extensions and aplurality of tabs provided on one of the wheel rim and the ring gear,the tabs extending in a direction of an axis of rotation of the wheel orthe ring gear.

The interface may be provided between:

-   -   one of the wheel and the ring gear; and    -   an interface connection member connected to the other of the        wheel hub and the ring gear.

The interface connection member may be a separate component of the wheelassembly. The interface connection member may preferably be a brake bar.

The connecting members may be fixed relative to one of the wheel and thering gear and radially movable relative to the other.

The connecting members may be fixed relative to one of the wheel and thering gear via screw threads.

The connecting members may be free to move relative to both the wheeland the ring gear.

At least one of the connecting members may provide a resilientconnection between the wheel and the ring gear.

A resilient spacer may be disposed on the connection path between thering gear and the wheel and may itself be disposed between the ring gearand the wheel.

The ring gear may be a roller gear, a sprocket or any other type ofdrive interfacing component for transmitting drive to or from the wheelhaving a substantially annular form.

The invention further provides a drive system for an aircraftundercarriage, comprising the wheel assembly of the invention.

Preferably, the drive system is detachably mounted on the landing gearmain leg. The drive system can therefore be removed for maintenanceand/or when the aircraft is to be used for long range operations whereit may not be economic to use the drive transmission due to its weightpenalty in cruise.

The drive system may be mounted externally on the landing gear on eitherthe sprung part (e.g. the strut) or on the un-sprung part (e.g. theslider or axle or bogie). The drive system may be pivotally mounted onthe landing gear. The output shaft carrying the drive pinion may rotateabout a substantially horizontal pivot axis displaced from the axis ofrotation of the drive pinion. The ring gear my be one of first andsecond gears which may move into and out of engagement by rotation aboutthe pivot axis. A motor of the drive system may move with the drivepinion about the pivot axis, or alternatively the motor may be staticwith respect to the pivot axis, or further alternatively the motor mayrotate about the pivot axis as the drive pinion moves through an arccentred on the pivot axis.

The drive pinion and/or the driven gear may include a constant-velocityjoint or similar device between the gear and the shaft on which it isrotatably mounted. This can help to ensure that the driving engagementcan be maintained as the landing gear deflects.

The landing gear may have only one driveable wheel. Alternatively, twoor more of the landing gear wheels may be driven by one or more motors.A differential may be used between the motor(s) and the drive pinions.The motor may be electric or hydraulic, for example.

The gear attached to the wheel preferably has a larger diameter than thedrive pinion to develop a significant torque magnifying gear ratio. Bymaking use of the large hub diameter in this way, a mass optimisedsolution can be achieved.

When incorporated on an aircraft, the landing gear may be used with apower and control system for supplying power to, and controllingoperation of, the drive transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 shows an isometric view of a drive system according to a firstembodiment:

FIG. 2 shows a further isometric view of the drive system of FIG. 1;

FIG. 3 shows an isometric view of selected components of a drive systemaccording to a second embodiment;

FIGS. 4 and 5 show schematic illustrations of deformation modes of awheel rim under load;

FIG. 6 shows ring gear mounting arrangement according to the invention;

FIGS. 7 and 8 show detail of the arrangement of FIG. 6;

FIG. 9 shows a wheel hub for the present invention;

FIG. 10 shows a ring gear for the present invention; and

FIGS. 11 and 12 show a ring gear connection member for the presentinvention.

FIG. 13 shows a schematic illustration of the fit of the interface wheelassembly of the invention.

DETAILED DESCRIPTION OF EMBODIMENT(S)

The illustrated embodiments are shown applied to an aircraft landinggear which has two wheels, but the principles of the embodiments may beapplied to landing gear with any number of wheels including only asingle wheel. The wheel and gear interface of the present invention maybe applied in any drive system to engage a corresponding sprocket orpinion. The illustrated embodiment can be applied to a main landing gear(i.e. a landing gear attached to wing structure or fuselage structure inthe region of the wings), since the weight supported by the main landinggear is considered to provide the best traction between the wheels andthe ground to enable reliable aircraft ground taxiing. However, a drivesystem incorporating the wheel assembly of the present invention mayalternatively be applied to a nose landing gear (i.e. a steerablelanding gear towards the nose of the aircraft). The main landing gearshown is applicable to a single aisle passenger airliner (approximately150-200 pax), although it will be appreciated that this invention haswide applicability to a variety of aircraft types and weights, includingcivil aircraft, military aircraft, helicopters, passenger aircraft (<50pax, 100-150 pax, 150-250 pax, 250-450 pax, >450 pax), freighters,tilt-rotor aircraft, etc.

The landing gear 10 illustrated in FIGS. 1 and 2 includes a telescopicshock absorbing main leg 12, including an upper telescopic part 12 a(main fitting) and a lower telescopic part 12 b (the slider). The uppertelescopic part 12 a is attached to the aircraft fuselage or wing (notshown) by its upper end (not shown). The lower telescopic part 12 bsupports an axle 14 carrying a pair of wheels 16, one on either side ofthe main leg (only one wheel 16 is shown in FIGS. 1 and 2, for clarity).The wheels 16 are arranged to rotate about the axle 14 to enable groundmovement of the aircraft, such as taxiing or landing.

Each wheel 16 comprises a tyre 17 supported by a hub 18 having a rim 18a at its outer edge which holds the tyre 17. A driven gear 20 isattached to the hub 18 (preferably at the rim 18 a) so as to berotatable with the wheel 16. The driven gear 20 may be attached to thewheel 16 by a plurality of discrete couplings, which may provide a rigidor flexible attachment. Alternatively, the attachment may be via aflange forming a continuous extension rim projecting axially from eitherthe wheel 16 or the driven gear 20.

The drive system 50 includes a motor 52 which transmits torque to adrive shaft 54 via a gearbox 70. The drive system 50 is supported by abracket 56 which is rigidly connected to the axle 14 of the landinggear. The bracket 56 includes two lugs comprising half moon clamps topermit ready attachment and detachment of the bracket 56 to the axle 14.The motor 52 is fixedly connected, e.g. by bolting, to the bracket 56.The gearbox 70 is pivotally connected to the bracket 56 at pivot lugs 82on each arm of the bracket 56 disposed either side of the gearbox 70.

A drive pinion 60 is mounted on the drive shaft 54 so as to be rotatableby the drive shaft about a drive axis. The drive pinion 60, drive shaft54 and gearbox 70 are pivotable by a linear actuator (positioner) 58,such as a direct drive roller screw electro mechanical linear actuator,extends between the bracket 56 (at an end nearest the axle 15) and thegearbox 70, or more particularly the housing 84 of the gearbox. Thus,linear movement of the actuator 58 is translated into rotationalmovement of the gearbox 70 and the sprockets 60 about the pivot 82. Thedrive system 50 can therefore be between a neutral configuration (notshown) in which the drive pinion 60 does not mesh with the driven gear20, and a driven configuration (shown in FIGS. 1, 2 and 3) in which thedrive pinion 60 is in meshed engagement with the driven gear 20. In theneutral configuration the wheel 16 is able to rotate freely, e.g. duringtake-off and landing, while in the driven configuration the wheel 16 canbe driven by the drive system 50, e.g. during ground taxiing.

In the embodiment of FIGS. 1 and 2 the driven gear 20 comprises a rollergear 34 and the drive pinion 60 comprises a sprocket. A roller gear is agear comprising a ring of rollers arranged around its periphery forengaging with teeth of a corresponding gear or sprocket, to transmitdrive therebetween.

The illustrated roller gear 34 can be formed by a rigid annular ring 35and a series of pins projecting from both sides of the annular ring 35to support the rollers mounted thereto. A first series of rollers 36 arotatably supported by the pins is provided on one side of the annularring 35, and a second series of rollers 36 b rotatably supported by thepins is provided on the other side of the annular ring. Each series ofrollers 36 a, 36 b extends around the annular ring to form a continuoustrack. First and second lateral annular rings 39 a, 39 b sandwich thefirst and second series of rollers 36 a, 36 b. The pins 38 supportingthe first series of rollers 36 a extend between the annular ring 35 andthe first lateral annular ring 39 a, and the pins 38 supporting thesecond series of rollers 36 b extend between the annular ring 35 and thesecond lateral annular ring 39 b. The annular ring 35 therefore forms acentral spine for supporting the pins which are cantilevered off thecentral spine. The annular ring 35 can comprise a plurality of axiallyextending connection extension tabs (not shown) providing mounting meansfor mounting the roller gear 34 to the hub 18. The annular rings 35, 39a and 39 b therefore act as roller mounting members for mounting therollers on the roller gear. Other mounting means according to theinvention, as will be described in greater detail in the following canbe used to mount the roller gear 34 to the hub 18.

The drive pinion 60 comprises a sprocket having two coaxial rings ofradially extending sprocket teeth which can interlock with the rollers36 of roller gear 34. That is, each ring of sprocket tee is arranged tomesh with one of the rings of rollers of the driven gear 20.

FIG. 3 shows an alternative, and preferred, embodiment in which thedriven gear 20 comprises a sprocket instead of a roller gear, and thedrive pinion comprises a roller gear instead of a sprocket. Thus, thedrive pinion comprises a roller gear 64 having two coaxial rings ofrollers and the driven gear 20 is replaced by sprocket 66 having twocoaxial rings of sprocket teeth. In all other respects the drive systemis identical to that described above with reference to FIGS. 1 and 2,and the features of the drive system described below apply equally toboth embodiments. The roller gear 64 may be constructed similarly to theroller gear 34, although of course it has a much smaller diameter andtherefore fewer rollers.

An advantage of the sprocket-roller gear arrangement is that it is moretolerant of wheel and axle deformation than meshing toothed geararrangements. Landing gear wheels and axles are subject to high loadsand consequential deformation during ground taxiing, and a driven gearfixed to the wheel will inevitably deform in response to suchdeformation. Meshing toothed gears are intolerant of such deformationand a typical toothed rim gear may need to be isolated from the wheelvia bearings, a flexible interface, or similar. In contrast, thesprocket and roller arrangement of the present invention may be able totolerate the deformation without such modification.

Such an arrangement also has the advantage of being lightweight andhaying high structural strength. The main failure mode of the rollers isvia shear failure of the pins; by mounting each roller directly on itsrespective pin, with no intermediate sleeve, bush or other part, thediameter of the pin can be maximised to maximise shear strength.

In variations to the embodiments described above, the drive pinion maybe formed as a sprocket having a single row of teeth, and the drivengear may be formed as a roller gear having a single row of rollers. In afurther variation, the drive pinion may alternatively comprise a singlering of rollers for engaging with a driven gear formed as a sprocket(not shown) having a single row of sprocket teeth.

Although the figures only show features of the drive system 50 fordriving one of the wheels 16, it is envisaged that these features may bemirrored for the other wheel 16. That is, it is envisaged that one drivesystem 50 may be provided for each wheel 16. For a landing gear 10 withfour or more wheels 16, a drive system 50 may be provided for each ofthe wheels 16, or for only two of them. In embodiments in which only twoof the wheels 16 are provided with drive systems 50, it may be necessaryto provide further motors (not shown) to achieve pre-landing spin-up ofthe un-driven wheels, with ground taxiing being accomplished by the twodrive systems 50. In other embodiments it may be possible to have onemotor 52 shared between two drive systems 50.

Although the figures only show the drive system 50 supported by abracket 56 which is rigidly connected to the axle 14 of the landinggear, the drive system 50 may alternatively be mounted on the uppertelescopic part 12 a (main fitting) or lower telescopic part 12 b(slider).

FIGS. 4 and 5 schematically illustrate different modes of deformationwhich can occur when a vehicle, in particular an aircraft, is carried bya wheel. Dashed line 401 illustrates a nominal wheel rim circumferencewhen no load is applied. Solid line 402 illustrates the phenomenon of“ovalisation”, which can occur when significant weight is applied to awheel at its axle, and reacted by the ground 403. Now considering thecase where the ring gear illustrated in FIGS. 1 to 3 is fixedly attachedto the rim of the hub of the wheel, it can be seen that the ring gearwill also deform with the wheel rim of the wheel. Such deformations canchange the radial distance from the axle 14 of the wheel to theperiphery of the ring gear 20 of FIG. 1. This can therefore causevariations in the required distance at which pinion gear 60 must be heldfrom the axle 14 in order to properly mesh with the ring gear 20. Thereis therefore a need to address this problem of ovalisation of the wheelhub.

FIG. 5 schematically illustrates a different deformation case, whereagain, dashed circle 401 illustrates a nominal form of a wheel rim in anun-loaded state. The solid line 502, illustrates, in an exaggeratedschematic manner, how a wheel hub can deform under significant loading.As illustrated, a degree of flattening can occur at the bottom edge nearthe ground 503 and this can also cause a slight deformation at the upperside of the wheel rim, where it can be seen that the solid line 502 isslightly below the dashed line 401.

Further, the wheel assembly will often be subject to heat cycles. Thiscan be due to ambient temperature changes, and also due to heatgenerated by braking assemblies held in the wheel, or mounted thereto.When braking a vehicle, brakes convert kinetic energy to heat energy andso the wheel and surrounding components can be caused to increase intemperature. The temperature cycles can be especially large in aircraft,since at cruising heights, the landing gear will generally be at verylow temperatures, well below freezing, and once the aircraft lands, thena large amount of heat is generated by braking the aircraft due to itslarge size and speed, which combine to result in a high level of kineticenergy to convert to heat and disperse from the braking system. This canlead to large changes in temperature of all components in the wheelassembly during normal use. These changes in temperature causecomponents to expand or contract and where different materials are used,then the components may change in dimensions by differing amounts,causing additional stresses in the components when they are fixedlyconnected. The wheel may be formed from lightweight alloys to minimiseweight, while the gears or sprockets mounted to the wheel may be formedof higher strength alloys or metals, such as steel, for example. Thermalexpansion can therefore cause stresses in these components when they arefixedly connected to one another.

In seeking to address these issues, the inventors have devised a novelinterface for connecting a ring gear to a wheel hub.

A wheel hub assembly comprising such a novel interface is illustrated inFIG. 6. The assembly 600 includes a wheel 601, which comprises a wheelrim 602, which is configured to carry a tyre. The rim 602 is arrangedaround a central hub portion 603 and, as illustrated schematically inFIGS. 4 and 5, when a load is applied to the wheel rim 602 via a tyre,from the ground, then the opposing force, transmitted via an axle towhich the wheel is mounted and via central hub portion 603, can causedeformation of the wheel rim 602. A ring gear 700 is mounted to thewheel 601, which comprises wheel rim 602 and a central wheel hub 603.

To isolate the ring gear 700 from deformation, in a radial direction, ofthe wheel rim 602, a radial clearance can be provided in an interfaceconnecting the ring gear 700 to the wheel rim 602. In the illustratedembodiment, this is provided by creating an internal diameter of thering gear 700 which is greater than an outer diameter of a flange orextended portion 604 of the wheel rim. This creates a certain amount ofradial free movement or “play” between the extension 604 and the ringgear 700. In this way, an interface providing a radial clearance, orfreedom of relative radial movement, can be provided, connecting thewheel and the ring gear. The illustrated flange 604, is provided as a‘grow-out’, or lateral extension of the wheel rim 602. This extension or‘grow out’ extends in a direction substantially parallel to therotational axis of the wheel. With such a clearance provided betweeninterfacing parts connecting the ring gear 700 to the wheel 601, it isnecessary to provide features which can transmit a torque between thewheel 601 and the ring gear 700. Such a torque must be provided in orderto allow a drive input provided to the ring gear to be transmitted tothe wheel to drive a vehicle to which the wheel assembly is fitted.Conversely, if the ring gear 700 is used for braking purposes, then itis necessary to transmit an opposing, braking, torque from the ring gearto the wheel 601 to brake the vehicle or aircraft to which the wheel isfitted.

The interface of the present invention provides for the transmission oftorque by providing, in at least one of the ring gear 700 and the wheel601, an array of openings, which are arranged in a substantiallycircular array around an axis of rotation of the ring gear or wheel, anda plurality of corresponding connecting members disposed in theopenings, and free to move relative to the openings. Each connector isoriented with a substantially radial longitudinal axis and is free tomove along that axis relative to the opening in which it is disposed, sothat movement either of the opening or of the connector, in a radialdirection relative to the axis of rotation of the wheel or ring gear, isnot transmitted to the other.

In the arrangement illustrated in FIG. 6, a plurality of openings areprovided in the flange 604, with a plane of the opening beingsubstantially perpendicular to a radius of the wheel and an axis passingthrough the opening being substantially radial with respect to thewheel. This arrangement of the openings is termed a radial orientation,since an axis passing through the openings is radial relative to thewheel or ring gear; these openings are considered radially oriented withrespect to the wheel or ring gear.

To prevent the connecting members located in the openings 606 from beingdislodged or falling out during use, the connecting members and theopenings can be provided with threads to retain the connecting membersin the openings 606. In an alternative arrangement, the connectingmembers may be free to translate through the openings 606 while threadsmay be provided on the ring gear 700 to connect the connecting membersto the ring gear 700. In a further alternative, the connecting membersmay be free to slide through openings in both the ring gear 700 and thewheel 601. To retain the connecting members from falling out or beingdislodged from the openings, the connecting members may, in this case,be provided with retaining means provided at each end, or between thewheel and ring gear, to movably retain them in the openings and preventthem from falling through the openings.

FIG. 7 illustrates further detail of the arrangement of FIG. 6. Here itcan be seen that the connecting members 607 are located in tabs 701extending laterally from the ring gear 700, extending laterally meaningextending in a direction of the axis of rotation of the ring gear 700.The arrangement could also be reversed, in that a flange equivalent tothe flange 604 may be located on the ring gear 700 instead of on thewheel 601 and tabs equivalent to the tabs 701 could be provided on thewheel 601, preferably at its rim 602, to provide the necessaryengagement via connecting members 607.

As an optional feature, one or more fixed or resilient retaining meansmay be provided in one or more of the openings, as illustrated by thenut and screw thread component 608 shown in FIG. 7. This may bebeneficial because, in the absence of any fixed or resilient connectionpoints, the ring gear 700 may have excessive freedom to move relative tothe wheel 601 and may vibrate or rattle excessively. Therefore, asubstantially fixed connection at at least one point 608 on thecircumference of the ring gear and the wheel assembly, or at more thanone point on the assembly, may be beneficial. However, configuring thisfixed connection as a completely rigid assembly may remove some or allof the benefits of the radial displacement which is enabled by the freeradial movement of connectors 607. Therefore, the connecting assembly608 may incorporate a resilient component in the connection path betweenthe ring gear and the wheel. This can allow radial displacement when acertain load is applied, so as to enable displacement of the ringrelative to the wheel rim at the point of the connector 608 at highloads. Such a high loading may be that induced by deformation of thewheel rim due to the loading examples illustrated in FIGS. 4 and 5. Sucha configuration may also resist significant movement under lightloading, such as that induced due to vibration or rotation of the wheelalone, to prevent excessive vibration or rattling of the ring gear 700on the wheel 601.

FIG. 8 illustrates further detail of the assembly of FIG. 6 with thefixed connection 608 illustrated from below, where a head of thethreaded element can be seen engaging the opening 606, through which thethreaded element passes. A resilient member may be located between theconnector 608 and the opening 606 to allow some resilient displacementin that connection between the wheel rim and the ring gear.

FIG. 9 illustrates a wheel 601 of the present invention, where theflange 604 can be seen without the ring gear 700 mounted to it, so thatthe locations of openings 606 can be more clearly seen, and the form ofthe grow-out, or lateral extension, created to provide the flange 604 onthe wheel rim 602 can also be seen.

The desired radial clearance or ‘play’ provided by the interface of theinvention can be provided in the manner illustrated in the describedembodiments, between the internal diameter of the ring gear 700 and anexternal diameter of the flange 604, but can also be provided byalternative arrangements. The desired radial freedom of movement can beprovided between any interfacing parts which provide a connectionbetween the ring gear and the wheel 601, and need not necessarily beprovided at the internal diameter of the ring gear 700, nor necessarilyat the external diameter of the flange 604. There may alternatively beprovided a series of tabs or extensions extending from the wheel rim, oralternatively extending from other features of the wheel. Connectionfeatures of the interface may be connected to intermediate features suchas ribs 605, or other components mounted to the wheel rim or to the ribs605, or to the hub 603. A common component of a wheel assembly of anaircraft which may provide this connecting function is a brake bar forcarrying brake components of the wheel assembly. A connecting member forproviding the interface of the invention may therefore be connected to abrake bar of a wheel assembly, or alternatively to another intermediatemember of the wheel assembly

FIG. 10 illustrates a ring gear 700 of the present invention, withconnecting members 607 located in openings in the tabs 701 provided onthe ring gear. As illustrated in FIGS. 7 and 8, one fixed connectormember 608 is located in one of the openings and can include a resilientmember to provide a resilient connection between the ring gear 700 andthe wheel 601.

FIGS. 11 and 12 show an example of a connector member which can be usedin the assembly of the illustrated embodiment. The connector member 100has a first portion 101, for location in an opening of the ring gear,and a second portion 102, for location in the openings of the wheel rim.One or the other of the first 101 and second 102 portions may beprovided with a thread for engagement with a corresponding thread of anopening or cavity in which it is to be located. A rotational drivefeature 103 may be provided to allow a tool to be inserted into theconnector member to rotate it for engagement with threads of thecorresponding opening or cavity in which it is to be fixedly attached.Whichever portion 101 or 102 is not threaded can be provided with asmooth outer surface and a small clearance fit may be provided betweenit and the opening in the corresponding ring gear or wheel, so that theconnector member can translate along its longitudinal axis relative tothe opening in which it is received, to provide the desired isolation ofthe ring gear from deformation of the wheel hub. In FIG. 12, a furtheralternative drive feature can be seen, for receiving a planar orcross-headed tool or screwdriver for rotating the connector member.

FIG. 13 shows a schematic illustration of how the invention functions toisolate the ring gear 700 from deformations in the wheel rim 602. A loadacting in the direction of arrow 131 causes the wheel rim to becompressed in the direction of that load and so the sides of the wheelhub bow outwardly in the direction of arrows 132. In this illustrationthe connecting members 607 are connected to the ring gear 700 and arefree to move inwardly and outwardly in openings connected to, or formedin, the wheel rim 602. In this way, the rim 602 can deform and the gear700 is substantially unaffected by that deformation. A torque in adirection of, or opposite to, arrow 134 can therefore be transferredbetween the ring gear 700 and the wheel rim 602. One or more resilientspacers 133 may be located on the connection path between the ring gearand wheel rim to prevent excessive movement of the ring gear under lowloading levels, to prevent unnecessary rattling or vibration asdescribed above. Connecting members 607 may have an elongate form andmay be, as illustrated in the previous figures, substantiallycylindrical, having a circular outer profile. One or more of theconnecting members may be integrally formed with the gear and/or thewheel.

A further degree of freedom can be provided by mounting one end of bothends of one or more of the connecting members in a spherical bearing,commonly referred to as a ‘rose joint’. This can allow the connectingmembers some angular deflection, as well as the longitudinal deflectionalong their longitudinal axes described above, with respect to the ringgear and/or wheel, depending upon where the spherical bearing or rosejoint is located.

It will therefore be appreciated that the clearance, or freedom ofradial movement, provided by the interface of the present invention canbe provided between a flange and a corresponding set of tabs orextensions provided on the wheel and ring gear of the invention. It canalternatively be provided between intermediate components attached tothe wheel and/or ring gear, or could further be provided between a pairof flanges or extensions 604 provided on each of the ring gear and wheelhub. The radially oriented openings, provided with connecting memberswhich can translate relative to at least one of the two components,allows the radial isolation of the ring gear from radial deformation ofthe wheel hub. Torque can be transmitted between the wheel hub and thering gear by creating a shear force in the radially oriented connectingmembers connecting the two components. Although openings passingentirely through the components are described in the Figures, suitableopenings may be cavities which allow for longitudinal movement of theconnecting members in the cavities.

In each of the arrangements described above the principle of achievingdrive via meshing between a sprocket and roller gear/roller chain can beapplied when the driven gear comprises the sprocket and the drive pinioncomprises the roller gear/roller chain, and vice versa.

Although the invention has been described above with reference to one ormore preferred embodiments, it will be appreciated that various changesor modifications may be made without departing from the scope of theinvention as defined in the appended claims.

The invention claimed is:
 1. A wheel assembly, comprising: a wheel; aring gear, mounted to and rotatable with the wheel; and an interface forconnecting the wheel hub to the ring gear to transmit a torquetherebetween; the interface comprising: an array of substantiallyradially oriented openings, arranged in a substantially circular arrayaround an axis of rotation of the assembly; and a plurality ofconnecting members disposed in the openings, each connector having asubstantially radially oriented longitudinal axis, the connectingmembers being free to move relative to at least one of the wheel hub andthe ring gear, to permit relative radial movement between the ring gearand the wheel hub; such that torque applied to one of the ring gear orthe wheel is transmitted to the other via the connecting members, andthe ring gear is substantially isolated from radial deformation of thewheel rim.
 2. A wheel hub assembly according to claim 1, wherein theinterface provides a radial clearance on a connection path between thewheel hub and the ring gear.
 3. A wheel hub assembly according to claim1, wherein the interface comprises a lateral extension to the wheel rimor ring gear, extending in a direction of the axis of rotation of thewheel or ring gear on which it is provided.
 4. A wheel hub assemblyaccording to claim 3, wherein the lateral extension comprises a grow-outprovided on at least one of the wheel and the ring gear.
 5. A wheel hubassembly according to claim 3, wherein the lateral extension comprises aseries of laterally extending tabs provided on one of the wheel or thering gear.
 6. A wheel assembly according to claim 3, wherein theinterface is provided between the lateral extensions and a plurality oftabs provided on one of the wheel rim and the ring gear, the tabsextending in a direction of an axis of rotation of the wheel or the ringgear.
 7. A wheel hub assembly according to claim 1, wherein theinterface is provided between: one of the wheel and the ring gear; andan interface connection member connected to the other of the wheel huband the ring gear.
 8. A wheel assembly according to claim 7, wherein theinterface connection member is a separate component of the wheelassembly.
 9. A wheel assembly according to claim 7, wherein theinterface connection member is a brake bar.
 10. A wheel assemblyaccording to claim 1, wherein the connecting members are fixed relativeto one of the wheel and the ring gear and radially movable relative tothe other.
 11. A wheel hub assembly according to claim 10 wherein theconnecting members are fixed relative to one of the wheel and the ringgear via screw threads.
 12. A wheel assembly according to claim 1,wherein the connecting members are free to move relative to both thewheel and the ring gear.
 13. A wheel hub assembly according to claim 1,wherein at least one of the connecting members provides a resilientconnection between the wheel and the ring gear.
 14. A wheel hub assemblyaccording to claim 13, comprising a resilient spacer disposed on theconnection path between the ring gear and the wheel.
 15. A wheel hubassembly according to claim 1, wherein the ring gear is a roller gear, asprocket or any other type of drive interfacing component fortransmitting drive to or from the wheel.
 16. A drive system for anaircraft undercarriage, comprising the wheel assembly of claim
 1. 17. Anaircraft, comprising the wheel assembly or drive system of claim
 1. 18.A drive system according to claim 16, wherein the drive system issupported by a bracket which is rigidly connected to an axle, mainfitting or slider part of a landing gear.
 19. A drive system accordingto claim 18, wherein the bracket includes two lugs comprising half-moonclamps to permit ready attachment and detachment of the bracket.